However, this is not a form of tropism, but a nastic movement, a similar phenomenon.

A response to a nondirectional stimulus, such as temperature or humidity, is a nastic movement.

The ethylene produced causes nastic movements of the leaves.

Both the leaves and the leaflets often have wrinkled pulvini to permit nastic movements.

The difference is that tropisms are influenced by the direction of their stimulus, while nastic movements are not.

Nyctinasty is the circadian rhythmic nastic movement of higher plants in response to the onset of darkness.

In tropisms, this response is dependent on the direction of the stimulus (as opposed to nastic movements which are non-directional responses).

In contrast to tropisms, nastic movements result from changes in turgor pressure within plant tissues, and may occur rapidly.

Thigmonasty or seismonasty is the nastic response of a plant or fungus to touch or vibration.

Nastic movements are non-directional responses to stimuli (e.g. temperature, humidity, light irradiance), and are usually associated with plants.

Nastic movements differ from tropic movements in that the direction of tropic responses depends on the direction of the stimulus, whereas the direction of nastic movements is independent of the stimulus's position.

Fundamental processes such as photosynthesis, respiration, plant nutrition, plant hormone functions, tropisms, nastic movements, photoperiodism, photomorphogenesis, circadian rhythms, environmental stress physiology, seed germination, dormancy and stomata function and transpiration, both parts of plant water relations, are studied by plant physiologists.